1. Field of the Invention
The present invention relates to vibration isolation devices that provide different degrees of stiffness in shear and compression to provide rotational stiffness in direction about one of the X, Y and Z axes of a sensor while permitting deflections in direction transverse to such axes.
2. Description of the Prior Art
In development of isolation devices, original concepts utilized a molded beam member comprising a pluralit of generally parallel, uniformly spaced plates or shims molded together with an elastomeric material. Connectors were provided at opposite ends. This work was originally reduced to practice by other than the present inventors and forms prior art to the invention herein under 35 USC 102(g).
However, such beam member did not provide the necessary isolation vibration in shear and stiffness in rotational direction about an axis for the sensor involved. The plates were evenly spaced along the beam length, and while two different spacings were used in experimenting, by merely adjusting the spacing it was not possible to attain a desired result wherein the beam member has a relatively low linear resonant frequency, for example 30 Hz and a substantially higher rotational resonant frequency, for example 200 Hz and hold the sway spacing to an acceptable level. When there is a substantial difference between the linear and rotational resonant frequencies, linear vibrations are substantially decoupled from the rotational vibrations. In other words, when sufficient rigidity in rotational direction about the Z axis of the sensor comprising the beams was obtained to raise the resonant frequency of mounting in such rotational direction, the resonant frequency of the second linear resonant mode in direction along the X, Y and Z axes was too high. Too little isolation of the sensor was provided at high frequencies.